Substance delivery device

ABSTRACT

A substance delivery device includes a combustible paperboard strip and at least one substance toxic to insects and a perfume. The delivery device can take the form of a coil and includes a flexible backing sheet for supporting the combustible paperboard strip. The flexible backing sheet is not capable of combustion. Additionally, the material of the paperboard strip can include a combustion promoter.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims priority under 35 U.S.C. § 365 fromInternational Application Serial No. PCT/1B00/00883, filed Jun. 29,2000, which claims priority from United Kingdom Application Serial No.9915805.6, filed Jun. 29, 1999, which are herein incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a substance delivery device comprisinga paperboard strip, which includes at least one of substance toxic toinsects or a perfume. The present invention also relates to a method formanufacturing such a device. More particularly, but not exclusively, thepresent invention relates to a mosquito coil comprising a paperboardcoil impregnated with a substance toxic to mosquitoes and a method ofmanufacturing the same.

U.S. Pat. No. 5,447,713 discloses a mosquito coil manufactured from woodfibres and/or wood chips and a binder. The mixture of ingredients ispressed to form a board from which the coils are punched. The woodfibres or chips remain discrete and separate and are held together bythe binder. The use of a binder to give the coil mechanical stabilitymeans that the coil tends to be brittle. A significant proportion ofcoils manufactured from such resin-bound boards are damaged eitherduring distribution or by subsequent handling by the consumer.

SUMMARY OF THE INVENTION

In a first aspect, the pre nt invention provides a substance deliverydevice comprising a combustible paperboard strip and at least one of asubstance toxic to insects and a perfume.

The term paperboard refers to fibrous structures which are made byfelting fibres from a fluid suspension. The felting process results inthe fibres becoming enmeshed with each other so providing a continuousmatrix. The presence of enmeshed fibres such as result from a feltingprocess can be detected by visual inspection of the product, optionallyusing magnifying apparatus such as a microscope. The resultingpaperboard is more flexible (and so less brittle) than known resin-boundboards. A delivery device manufactured from such a paperboard is lesslikely to be damaged during packing, transit or subsequent handling thandevices made by processes involving compression of fibres with a resinbinder.

Known resin-bound delivery devices also tend to “dust” in that smallparticles tend to break from the coil during handling. This leaves afine powder on the hands of the user and on any other surfaces withwhich the coil has been in contact. A significant mass of the coil canalso be lost during transit through dusting leading to a reduction inthe performance of the coil. The delivery device of the invention hasthe advantage that it has a reduced tendency to form “dust”.

The delivery device of the invention can also be significantly lighterthan known devices in which cellulose fibres are bound together by aresin, while still burning for the same amount of time. This can reducedistribution costs.

The use of a paperboard material in the delivery device of the inventionmeans that the device can be produced in a wide range of colours byselection of a material on which images can be formed, for example usinginks, for example by printing or other techniques. Known devices madefrom materials other than paperboard tend only to be produced in alimited range of colours, typically green or black, in some casesbecause of difficulties associated with printing on resin materials.

Preferably, the fibres comprise materials which are known for use inpaper making, especially cellulosic fibres, more preferably waste paperfibres, especially kraft pulp. The papermaking fibre can be primary orsecondary papermaking fibre. This makes the resulting delivery devicerelatively inexpensive to produce.

The fibres can comprise wood free fibres, preferably at least one ofbagasse, straw or bamboo. This improves the flexibility of the resultingpaperboard strip.

The fibres that are used to form the paperboard need to be long enoughthat they can mesh together to form a mechanically stable structure inwhich the fibres are largely retained without the use of an additionalbinder such as a resin material. The characteristics of suitable fibreswhich can form such a stable structure are known within the paperindustry. Preferably, the length of the fibres that are used in thedevice of the present invention is at least about 0.1 mm, morepreferably at least about 0.3 mm, especially at least about 1.0 mm. Thelength of the fibres can be greater than this for some applications, forexample up to about 6.0 mm.

The fluid from which the fibres are felted can be aqueous based; wateris particularly preferred.

Preferably, the strip is in the form of a coil. The coil will usually behelical so that the strip burns along a helical path. A strip can beformed with a helical configuration by stamping from a sheet.

The delivery device can include a flexible backing sheet for supportingthe combustible paperboard strip. For a large range of strip widths,lengths and thicknesses, the paper-board strip might not be selfsupporting. Inclusion of such a backing sheet allows strips which arenot self supporting, but which otherwise have satisfactory physical andburn characteristics, to be used. It also enhances the mechanicalstability of the device.

The material of the flexible backing sheet can be selected so that it isnot capable of self sustaining combustion. This prevents the backingsheet from burning faster than the paperboard strip. Preferred materialsare paper-based, optionally treated with a flame retardant agent.Suitable flame retardant agents are known. However, it has been foundsurprisingly that little or no flame retardant agent need be applied toa paper-based backing sheet, to prevent it from burning faster than thepaperboard strip, if the flammability of the paperboard strip iscontrolled appropriately, for example by control of the density of thestrip and by use of combustion promotors and flame inhibitors.

The paperboard strip can include one or more combustion promoters. Thepromoter can be inherently combustible material, especially an organicmaterial, for example a charcoal powder. The promoter might promotecombustion in other ways, such as for example in the case of anoxidizing agent which can release of oxygen. An example of such anoxidizing agent is potassium nitrate. The charcoal powder or othercombustion promoter is preferably present in the paperboard in an amountfrom about 0.25 to 10% by weight of the dry paperboard strip, morepreferably from 0.5 to about 5%, for example from about 1 to about 2%.

The paperboard strip can include a dye, preferably an organic dye. Thedye can function as a combustion promoter as well as affecting thevisual appearance of the strip. The dye can preferably comprise 0.01% to10% more preferably 0.5% to 2% by weight of the dry paperboard strip.Addition of the dye makes the combustion of the paperboard stripresistant to being extinguished by external factors such as a breeze. Italso makes combustion insensitive to variations in internal propertiesof the paperboard strip.

The dye or other combustion promoter should preferably be distributeduniformly throughout the volume of the paperboard strip. Thedistribution of the dye has an impact on the combustion properties ofthe paperboard.

The paperboard can include one or more flame inhibitor agents. Thesewill generally be particulate materials which are inherentlynon-combustible at temperatures encountered when the device of theinvention is in use. Examples of suitable inhibitor agents includeparticulate inorganic materials such as calcium carbonate. The flameinhibiting properties of the agent can be affected by the size of theparticles. In many cases, smaller particles will enhance the flameinhibiting effect. Preferably, at least 90% of the particles passthrough a 150 μm aperture size mesh, more preferably through a 100 μmmesh, especially a 75 μm mesh.

The quantity of the flame inhibitor agent that is incorporated into thepaperboard will depend on issues such as its particle size, the densityof the board, the desired burn rate, and the presence and effect of anycombustion promotors. Preferably, the flame inhibitor agent is presentin an amount of at least about 1% by weight based on the weight of thedry fibre in the board, more preferably at least about 3%, for exampleabout 5%. The amount of the flame inhibitor agent will generally be lessthan about 30% by weight based on the weight of the dry fibre in theboard.

The paperboard strip can have a substantially rectangular cross section,the thickness of the strip preferably being in the range 0.2 to 1.9 mm,more preferably in the range 0.6 to 1.8 mm, the width of the strippreferably being in the range 2 to 6 mm, more preferably in the range 5to 6 mm. Such paperboard strips can exhibit a substantially uniform burnrate and are not prone to self extinguish.

Preferably the density of the paperboard strip is at least 400 kg.m⁻³,more preferably at least 550 kg.m⁻³. Preferably its density is not morethan 1000 kg.m⁻³, more preferably not more than 850 kg.m⁻³, especiallynot more than 750 kg.m⁻³, for example not more than 650 kg.m⁻³. Thedensity can be controlled during the manufacture of the paperboard, forexample by processes such as calendering.

Properties that are affected by the density of the paperboard includeoverall weight, burn rate, flexibility and mechanical stability of thestructure. A relatively high density can be preferred for manyapplications because of the mechanical stability of the structure whichallows it to be flexed without losing fibrous material. A high densityalso results in a reduced burn rate. However, the density should not beincreased to such an extent that a flame tends to self-extinguish, forexample when exposed to a draught.

In a further aspect of the invention there is provided a method ofmanufacture of a substance delivery device comprising the steps of:

-   -   adding a furnish comprising fibrous structures to a fluid to        form a fluid suspension;    -   felting the fibrous structures from the fluid suspension to form        a structure which comprises a mesh of interlocked fibres;    -   drying the mesh to form a paperboard; and    -   adding at least one of a substance toxic to insects or a perfume        to the paperboard.

The resulting delivery device is flexible and so is less likely to bedamaged than known devices either during transit or whilst being handledby the consumer. The invention includes substance delivery devices madeby the method.

The method of the invention should preferably result in a device with arelatively low density, and the pressure that is applied to the fibresduring the method, and the other conditions during manufacture of thedevice, should be selected accordingly. Generally, the method willinclude a step of calendering the fibres to reduce the thickness of thedevice. Preferably, the density of the finished device, after it hasbeen dried, is not more than 1000 kg.m⁻³, more preferably not more than850 kg.m⁻³, especially not more than 750 kg.m⁻³, for example not morethan 650 kg.m⁻³.

Preferably the method includes a step of cutting the paperboard to forma strip, more preferably a coil, especially a helical coil.

Preferably, the method includes a step of attaching the paperboard to aflexible backing sheet, especially by means of an adhesive. The step offastening the paperboard to the backing sheet should preferably takeplace after the mesh of interlocked fibrous structures has been formed,more preferably after the mesh has been at least partially dried to forma paperboard. The method can also include a step of drying the adhesivewhilst restraining the paperboard and backing sheet to preventdistortion of the paperboard.

The furnish can comprise waste paper, preferably at least one of kraftpulp or newspaper waste. This makes the resulting delivery devicerelatively inexpensive to produce. It can also reduces the weight of thedevice.

The furnish can comprise wood free fibres, preferably at least one ofbagasse, straw or bamboo. The use of wood free fibres rather than woodpulp is environmentally friendly.

The method can include a step of adding at least one of charcoal powderor a dye preferably an organic dye, to the fluid suspension. Preferablythe dye is saturated or impregnated into the paper board. This improvesthe combustion properties of the resulting coil.

The method can include the step of adding a dye to the paperboard,preferably by saturation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only, withreference to the accompanying drawings in which:

FIG. 1 shows a mosquito coil according to the invention in plan view;

FIGS. 2( a) to 2(d) show further embodiments of mosquito coils accordingto the invention in plan view;

FIG. 3 illustrates the variation in burn rate with thickness for arectangular paperboard strip of a mosquito coil according to theinvention;

FIG. 4 illustrates the variation in burn rate with width for arectangular paperboard strip of a mosquito coil according to theinvention;

FIG. 5 shows the variation in burn rate with density for a paperboardstrip of a mosquito coil according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a mosquito coil according to the invention. The mosquitocoil comprises a backing sheet 1 and a paperboard coil 2. The backingsheet 1 is a flexible paper sheet. The role of the backing sheet 1 isthreefold: firstly, it provides reinforcement for the paperboard coil 2so producing a dimensionally stable, flat, easy to handle coil;secondly, it enhances the performance of the coil by cutting off the airsupply to one side of the paperboard coil 2 from one side. This canreduce the burn rate of the paperboard coil 2 by as much as 20%;thirdly, it serves as a medium for branding or other product informationto be carried on the product.

The paper backing sheet 1 can be treated with a flame retardant additiveto make it incapable of self sustaining combustion. Such an additive canbe applied as a liquid by spraying. When the paperboard coil 2 is litthen the portion of the backing sheet 1 proximate to the burning end ofthe paperboard coil 2 can burn. However, because the backing sheet 1cannot itself sustain combustion, combustion of the backing sheet 1 willnot spread to areas of the backing sheet remote from the burning end ofthe paperboard coil 2. The combustion of the backing sheet 1 willtherefore closely follow the paperboard coil 2, and it will not trackacross the backing sheet 1 away from the paperboard coil 2. It cantherefore burn at the same rate as the paperboard coil 2.

The paper backing sheet 1 is manufactured from newsprint stock. This hasthe advantage that it can be coloured easily, for example using inks byprinting techniques. It also combines a good rigidity with low weightcharacteristics. The low weight of the backing sheet 1 significantlyreduces the cost associated with distribution of the mosquito coil. Theunit weight of the paper backing sheet 1 is chosen to lie within therange about 30 to 300 g.m⁻², for example about 55 g.m^(−2.)

In order to manufacture a paperboard coil, a furnish which consistsmainly of waste paper is taken and slushed along with an unbleachedkraft pulp and newspaper waste. Wastepaper containing predominantly woodfree fibres is used, for example fibres from bagasse, straw or bamboo.Such fibres give the resulting paperboard an suitable strength anddensity. Wood free fibres are also relatively inexpensive. A typicalcomposition of the furnish is shown in table 1.

TABLE I Furnish Dry weight (%) Waste paper (high % of wood free fibre)75 Unbleached wood pulp 10 Newsprint waste 15

The slushing is done in water at a consistency of 2.5% in a hydropulper,according to established techniques used in the papermaking industry.After disintegrating the furnish so that an evenly mixed slurry of thefibre is obtained, an inorganic filler (for example calcium carbonate)is added and dispersed evenly by known methods. Immediately after thisthe pH of the mixture is raised to between 7 and 8 by, for example, theaddition of sodium aluminate.

The slurry is then passed through a mild refining process well known inthe papermaking art which results in a well dispersed fibre. Afterrefining a solution of a cationic retention aid, (for example Sursolan™K12L of BASF) is added which has the effect of fixing the inorganicfiller to the fibre.

Optionally an organic dye can be added to the slurry, or preferablyimpregnated into the paperboard to enhance both the colour and burningcharacteristics of the final paperboard. Paperboards having an organicdye concentration in the region of 0.01 to 10% of the weight of thepaperboard are to be preferred as this makes the combustion of thepaperboard far more resistant to being extinguished by external factorssuch as a breeze. It also makes combustion more insensitive to internalproperties of the paperboard.

Optionally, a charcoal powder can be added to the slurry duringmanufacture of the paperboard, to function as a combustion promoter, forexample in an amount of about 2 to 5% by weight of the dry paperboard.

The slurry is then diluted to about 0.6% consistency and pumped to theheadbox of a papermaking machine. The fibres are then felted fromsolution to form a mesh. The mesh is finally dried on conventionalpapermaking cylinders to form paperboard and sheeted at the end of theprocess.

By known papermaking techniques the density of the paperboard producedby the paper making machine is controlled to a target density of 0.55g.cm⁻³ and a thickness of 1.5 mm. Other thicknesses and densities arepossible as discussed below.

A coil of the desired shape is then punched from the paperboard sheetand coated with an insect repellant. Coating can be done by knowncoating or printing techniques. One example of such a technique is tospray the coil with insect repellant and then allow it to dry. Theresulting coil has an ash content of 3.4×10⁻⁵ kg.m⁻¹ (0.00034 g.cm⁻¹)and a burn rate of approximately 6.6×10⁻⁵ m.s⁻¹ (0.4 cm.min⁻¹). Examplesof suitable insect repellant materials include pyrethroid insecticidessuch as pyrethrum, resmethrin, bioallethrin, allethrin and mixturesthereof; specific examples include pynamin forte, esbiothrin and naturalpyrethrin. Other examples of insect repellant materials includecitronella, lemon grass oil, lavender oil, cinnamon oil, clove oil,sandalwood oil and the insect growth regulator hydroprene. Perfumes canalso be incorporated into the paperboard, for example with the insectrepellant.

The paperboard coil 2 is adhered to the backing sheet 1 by an aqueousadhesive such as a starch or dextrin adhesive, typically with a solidscontent in the range 5% to 10%. The drying of the adhesive will causethe backing sheet 1 to shrink and the paperboard coil 2 to distort. Toprevent this the paperboard coil 2 and backing sheet 1 are held underpressure between two plates in the form of a moving conveyor and thebottom plate is heated slightly to dry out the adhesive. Other types ofadhesive can be used.

The paperboard coil 2 shown in FIG. 1 has a total length of 1.8 m, astrip width of 5 mm and a burn rate of 6.6×10⁻⁵ m.s⁻¹ (0.4 cm.min⁻¹).The coil will therefore burn for about 7.5 hours.

Shown in FIGS. 2( a) to 2(d) are a number of other embodiments ofmosquito coils according to the invention.

The paperboard coil 2 of the mosquito coil shown in FIG. 1 has arectangular cross section. The width, thickness and density of thepaperboard coil 2 greatly influence the burn rate.

Shown in FIG. 3 is a graph of (burn rate)⁻¹ vs paperboard coil thicknessat a constant coil width of 5 mm and a density of 570 kg.m⁻³ (0.57g.cm⁻³). As the thickness of the paperboard coil is increased towards1.8 mm, the (burn rate)⁻¹ increases from 6000 s.m⁻¹ to 15000 s.m⁻¹ (1min/cm to 2.5 min/cm). At thicknesses larger than this the burnperformance becomes uncertain with a marked tendency for the flame toextinguish itself. Mosquito coils of the invention have paperboard coils2 having an optimum thickness of 1.5 mm, although paperboard coils 2having thicknesses in the range 0.2 to 1.9 mm (more preferably in therange 0.6 to 1.8 mm) perform well.

Shown in FIG. 4 is a graph of (burn rate)⁻¹ vs paperboard coil width ata constant thickness of 1.5 mm and a density of 570 kg.m⁻³ (0.57g.cm⁻³). As can be seen, the burn rate drops as the coil widens, withthe optimum width being reached at 5 to 6 mm. Thereafter the burn ratebecomes uncertain with a marked tendency of the flame to extinguishitself. Coil widths in the range 2 to 6 mm (more preferably in the range5 to 6 mm) perform well.

Shown in FIG. 5 is a graph of the inverted burn rate (burn rate⁻¹) vspaperboard coil density. As the density increases the porosity of theboard is reduced causing the burn rate to lessen to the point of theflame being extinguished. As shown in FIG. 4 the burn rate slows downwith increasing density until it is optimised at a density ofapproximately 550 kg.m⁻³ (0.55 g.cm⁻³). Thereafter the increase inpaperboard density has only a very small to negligible impact on theburn rate up to a density of 740 kg.m⁻³ (0.74 g.cm⁻³). Paperboard coilsaccording to the invention typically have densities in the range 400 to700 kg.m⁻³ (0.4 to 0.75 g.cm⁻³). Densities in the range 550 to 650kg.m⁻³ (0.55 to 0.65 g.cm⁻³) are to be preferred.

Whilst the above description reference has only been made to a deviceincluding an insect repellant, it is to be understood that the insectrepellant can be replaced by or included together with a perfume.

1. A substance delivery device comprising a combustible paperboard stripand at least one of a substance toxic to insects and a perfume, whereinsaid paperboard strip is formed from felting fibres from solution,wherein the density of said paperboard strip is not more than about 1000kg.m⁻³, the thickness of the strip being at least about 0.2 mm and notmore than about 6 mm and said at least one substance can be delivered bycombustion of said device.
 2. A delivery device as claimed in claim 1,in which the strip is in the form of a coil.
 3. A delivery device asclaimed in claim 1 or claim 2, which includes a flexible backing sheetfor supporting the combustible paperboard strip.
 4. A delivery device asclaimed in claim 3, in which the flexible backing sheet is not capableof self sustaining combustion.
 5. A delivery device as claimed in claim1, in which the material of the paperboard strip includes a combustionpromoter.
 6. A delivery device as claimed in claim 5, in which thecombustion promoter is distributed substantially uniformly throughoutthe paperboard strip.
 7. A delivery device as claimed in claim 1, inwhich the combustion promoter comprises a charcoal powder, the charcoalpowder preferably being present in the paperboard at about 1 to 10% byweight of the dry paperboard.
 8. A delivery device as claimed in claim1, in which the paperboard strip has a substantially rectangular crosssection, the thickness of the strip being at least about 0.2 mm and notmore than about 1.9 mm.
 9. A delivered device as claimed in claim 8, inwhich the width of the strip is at least about 2 mm and not being morethan about 6 mm.
 10. A delivery device as claimed in claim 1, in whichthe density of the paperboard strip is at least about 400 kg.m⁻³.
 11. Amethod of manufacture of a substance delivery device comprising thesteps of adding a furnish comprising fibrous structures to a fluid toform a fluid suspension; felting the fibrous structures from the fluidsuspension to form a mesh of interlocked fibrous structures; drying themesh to form a paperboard; and, adding at least one of a substance toxicto insects or a perfume to the paperboard, and cutting the paperboard toform at least one strip, wherein the density of the paperboard strip isnot more than about 1000 kg.m⁻³, the thickness of the paperboard stripbeing at least about 0.2 mm and not more than about 6 mm, and at leastone substance can be delivered by combustion of said strip.
 12. A deviceas claimed in claim 1, wherein said substance toxic to insects is atleast one substance selected from the group consisting of a pyrethroidinsecticide, citronella, lemon grass oil, cinnamon oil, clove oil,sandalwood oil, and an insect growth regulator.
 13. A method as claimedin claim 11, wherein said substance toxic to insects is at least onesubstance selected from the group consisting of a pyrethroidinsecticide, citronella, lemongrass oil, cinnamon oil, clove oil,sandalwood oil, and an insect growth regulator.
 14. A method as claimedin claim 11, which includes the step of attaching the paperboard to aflexible backing sheet.
 15. A method as claimed in claim 14, in whichthe backing sheet is attached by means of an adhesive, and in which themethod includes the step of drying the adhesive while restraining thepaperboard and backing sheet to prevent distortion of the paperboard.16. A method as claimed in claim 11, in which the furnish compriseswaste paper.
 17. A method as claimed in claim 11, in which the furnishcomprises wood free fibers.
 18. A method as claimed in claim 11, whichfurther comprises the step of adding a combustion promoter to the fluidsuspension.
 19. A method as claimed in claim 18, wherein the combustionpromoter comprises at least one of a charcoal and an organic dye.
 20. Aninsect repellant device comprising a combustible paperboard strip whichincludes a substance toxic to insects, wherein said paperboard strip isformed from felting fibres from solution, wherein the density of saidpaperboard strip is not more than about 1000 kg.m⁻³, the thickness ofthe strip being at least about 0.2 mm and not more than about 8 mm, saidat least one substance toxic to insects can be delivered by combustionof said device, and said substance toxic to insects is at least onesubstance selected from the group consisting of a pyrethroidinsecticide, citronella, lemon grass oil, cinnamon oil, clove oil,sandalwood oil, and an insect growth regulator.
 21. A method ofmanufacture of an insect repellant device comprising the steps of:adding a finish comprising fibrous structures to a fluid to form a fluidsuspension; felting the fibrous structures from the fluid suspension toform a structure which comprises a mesh of interlocked fibres; dryingthe mesh to form a paperboard; cutting the paperboard into at least onestrip and, adding a substance toxic to insects to the paperboard,wherein the density of said paperboard strip is not more than about 1000kg.m⁻³ and said strip being of a density and thickness capable ofmaintaining combustion of itself after combustion is initiated, whereinsaid at least one substance toxic to insects can be delivered bycombustion of said device and said substance toxic to insects is atleast one substance selected from the group consisting of a pyrethroidinsecticide, citronella, lemon grass oil, cinnamon oil, clove oil,sandalwood oil, and an insect growth regulator.
 22. A delivery device asclaimed in claim 5, in which the combustion promoter is comprised of anorganic dye.
 23. A method as claimed in claim 11 wherein the step ofcutting the paperboard to form a strip forms a strip is in the form of acoil.
 24. A method as claimed in claim 17 wherein the wood free fibersare comprised of straw.
 25. A method as claimed in claim 17 wherein thewood free fibers are comprised of bamboo.
 26. A delivery device asclaimed in claim 1, in which the paperboard strip has a substantiallyrectangular cross section, the thickness of the strip being at leastabout 0.6 mm and not more than about 1.8 mm.
 27. A delivery device asclaimed in claim 1, in the which the width of the strip is at leastabout 5 mm and not more than about 6 mm.
 28. A delivery device asclaimed in claim 1, in which the density of the paperboard strip is atleast, about 550 kg.m⁻³ and not more than about 650 kg.m⁻³.
 29. A methodas claimed in claim 16 wherein the waste paper is comprised of kraftpulp.
 30. A method as claimed in claim 16 wherein the waste paper iscomprised of newspaper waste.
 31. A method as claimed in claim 17wherein the wood free fibers are comprised of bagasse.